cardiac contractility modulating (CCM) devices are devices which modulate the activity of excitable tissues by application of non-excitatory electrical field signals to the excitable tissue through suitable electrodes in contact with the cardiac tissue. For example, CCM devices may be used, inter alia, to increase or decrease the contractility of cardiac muscle in vitro, in vivo and in situ. as disclosed in detail in PCT application PCT/IL97/00012 (International Publication Number WO 97/25098) to Ben-Haim et al., titled “ELECTRICAL MUSCLE CONTROLLER”, incorporated herein by reference. Other methods and applications of CCM devices are disclosed in PCT application PCT/IL97/00231 (International Publication Number WO 98/10828) titled “APPARATUS AND METHOD FOR CONTROLLING THE CONTRACTILITY OF MUSCLES” to Ben Haim et al., incorporated herein by reference, PCT application PCT/IL97/00232 (International Publication Number WO 98/10829) titled “DRUG-DEVICE COMBINATION FOR CONTROLLING THE CONTRACTILITY OF MUSCLES” to Ben Haim et al., incorporated herein by reference and PCT application PCT/IL97/00233 (International Publication Number WO 98/10830) titled “FENCING OF CARDIAC MUSCLES” to Ben Haim et al., incorporated herein by reference, PCT application PCT/IL97/00235 (International Publications Number WO 98/10831) to Ben Haim et al., titled “CARDIAC OUTPUT CONTROLLER”, incorporated herein by reference.
Further applications of the CCM including devices combining cardiac pacing and cardiac contractility modulation are disclosed in PCT Application, International Publication No. WO 98/10832, titled “CARDIAC OUTPUT ENHANCED PACEMAKER” to Ben Haim et al., co-assigned to the assignee of the present application. Such CCM devices function by applying to selected cardiac segments electrical signals of suitable amplitude and waveform, appropriately timed with respect to the heart's intrinsic electrical activity or with respect to paced cardiac electrical activity. The contraction of the selected segments can be modulated to increase or decrease the stroke volume of the heart. The timing of the CCM signals must be carefully controlled since application of the CCM signal to the myocardium at inappropriate times may be arrhythmogenic. The CCM signal must therefore be applied to the selected cardiac region within a defined time interval during which the selected cardiac region will not be stimulated by the CCM signal.
As disclosed in International Publication No. WO 98/10832, the ETC signal may be timed relative to a trigger signal which is also used as a pacing trigger, or may be timed relative to locally sensed depolarizing electrogram signals.
Timing of the delivery of CCM signals relative to the time of detection of locally sensed electrogram signals may present certain practical problems. For example, triggering of the CCM signal by any locally detected depolarizing signals irrespective of the time of detection of the depolarizing signal within the cardiac beat cycle, may increase the probability of spurious detection of noise signals or of ectopic beats such as premature ventricular contractions (PVCs) or the like, which may lead to delivery of improperly timed and potentially arrhythmogenic CCM signals. It is therefore desirable to have a method for determining proper timing of the delivery of CCM signals without unduly increasing the probability of delivering an improperly timed CCM signal caused by spurious noise detection or by detection of ectopic beats.
One approach used for to detecting suspected events such as ectopic beats is to use a combination of sensing leads, typically including an atrial lead (as well as one or more ventricular leads to detect such events. Sensing the electrical events recorded simultaneously by ventricular and atrial leads provides information based inter alias, on the signal shape, duration and timing. This multiple lead information may be processed using a variety of detection and decision algorithms) and used to differentiate between normal cardiac events (such as intrinsically naturally initiated ventricular pacing and ectopic or other abnormal forms of cardiac electrical events (such as, for example PVCs). When such a suspected abnormal cardiac event is detected, the delivery of a CCM signal within the current beat cycle (and optionally within one or more of the following beat cycles) is inhibited.
However, the use of multiple leads including an atrial lead complicates and often increases the time required for lead placement.
Typically, about 35% of cardiac patients are diagnosed with Atrial fibrillation (AF) or paroxysmal AF or are candidates to develop AF. Currently, the treatment of such patients with supra-ventricular paroxysmal cardiac disorders present a challenge for CCM therapy as current ectopic beat detection methods and algorithms do not enable differentiating between temporally abnormal electrical activity due to an ectopic beat propagating from a lateral ventricular focus and an abnormally timed beat resulting from paroxysmal atrial activity. As a result many of the patients with AF or belonging to a group with increased probability for developing AF are not candidates for CCM therapy using a CCM device. Furthermore, if a patient already having an implanted CCM device develops AF, the CCM therapy is inhibited whenever an atrium is arrythmogenic. This situation is undesirable, as the benefits of CCM therapy cannot be delivered to the ventricles while any atrial arrythmogenic activity is detected.
Another problem which may arise in the use of CCM devices is that a CCM device may often be implanted in a patient which has a previously implanted pacemaker. In such a situation the pacemaker of the patient may or may not pace the heart of the patient, independently. Such independent pacing is not synchronized with the activity of the CCBM device. In such a case, if the CCM is expected to timely and safely deliver CCM signals to the heart, the CCM device must be able to recognize the pacing of the heart by the independent pacemaker and to suitably detect the pacing and to suitably adapt the CCM delivery parameters in accordance with the pacemaker activity.
It may therefore be advantageous to be able to safely deliver ventricular CCM signals to a patient's heart in the presence of AF as well as to safely and effectively deliver CCM signals to the heart of patients having an independent implanted pacemaker.